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Exploring Objects in Motion

Physics is a science that is based upon experimental observations. Many of the basic principles used to describe and understand mechanical systems, such as objects in linear motion, can be applied later to describe other more complex natural phenomena. How can you measure the speed of the vehicles in a video clip?

QuestionWhat type of measurements could be made to find the speed of a
vehicle?

The video footage was taken in the midwestern United States
at approximately noon. Along the right shoulder of the road are
large, white, painted rectangles. These types of markings are
used in many states for aerial observation of traffic. They are
placed at 0.322-km (0.2-mi) intervals.

Observe What type of measurements might be
taken? Print the Data
Table. Record your observations of the surroundings, other
vehicles and markings in the Data
Table. On what color vehicle is the camera located, and what
color is the pickup truck in the lane to the left?

Measure and Estimate View the video again and look
for more details. Is the road smooth? In what direction are the
vehicles heading? How long does it take each vehicle to travel two
intervals marked by the white blocks? Record your observations and
data in the Data Table.

Summarize your qualitative observations.

Summarize your quantitative observations.

Make and Use Graphs Graph both sets of
data on one pair of axes.

Estimate What is the speed of the vehicles
in km/s and km/h?

Predict How far will each vehicle travel
in 5 min?

Measure What is the precision of the
distance and time measurements?

Measure What is the precision of your
speed measurement? On what does it depend?

Use Variables, Constants, and Controls
Describe the independent and the dependent variables in
this experiment.

Compare and Contrast Which vehicle's
graph has a steeper slope? What is the slope equal to?

Infer What would a horizontal line mean
on the graph? A line with a steeper slope?

Speed is distance traveled divided by the amount of time
to travel that distance. Explain how you could design your
own experiment to measure speed in the classroom using remote-controlled
cars. What would you use for markers? How precisely could
you measure distance and time? Would the angle at which
you measured the cars passing the markers affect the results?
How much? How could you improve your measurements? What
units make sense for speed? How far into the future could
you predict the cars' positions? If possible, carry out
the experiment and summarize your results.

When the speedometer is observed by a front-seat passenger,
the driver, and a passenger in the rear driver's-side seat,
readings of 90 km/h, 100 km/h, and 110 km/h, respectively,
are observed. Explain the differences.

Share Your Data

Post your experiment in the Share
Your Data fields for measuring speed in the classroom using remote-controlled
cars. Include your list of materials, your procedure, and your predictions
for the accuracy of your lab. If you actually perform your lab, post your
data and results in the Data Table below. See example.